Saudi-led forces have launched an assault on the key port of Hudaydah after Houthi rebels ignored a final deadline to withdraw, reports say.

Rebel positions are being bombarded from the air and sea, according to regional media.

Aid agencies have warned the move will cause a humanitarian catastrophe as it will cut off vital supply lines and directly endanger the lives of up to 200,000 people living in the city.

The port is the main entry point for humanitarian aid into Yemen, and more than seven million people in the war-torn country are dependent on food aid.

As much as 80% of the aid, including medicines, fuel and food that reaches the famine-struck country, goes through the port, but the Saudi coalition claims the Iranian-backed Houthis use the port both to smuggle arms and raise taxes, prolonging the conflict.

The Saudi-owned Al-Arabiya network reported that the "liberation" of Hudaydah had begun with a large-scale ground assault supported by air and naval cover.

The Saudi coalition, including the United Arab Emirates, mercenaries, and indigenous Yemeni forces, were mounting an air, naval and land assault designed to dislodge the Houthis.

Explosions were heard on the outskirts of the port city, it added.

The Yemeni government of President Abdrabbuh Mansour Hadi said in a statement that all political means to persuade the rebels to withdraw had been exhausted.

The UAE foreign minister Anwar Garhgash said the coalition had given the Houthi forces nearly three days to leave the port or face an attack. “The Houthis cannot hold Hodeidah hostage to finance their war and divert the flow of humanitarian aid. Their assault on the Yemeni people has continued for too long. Their folly of trying to take over Yemen through the barrel of a gun is coming to an end”.

United Nations diplomats, backed by the British and the US, have spent days pressing the UAE and Saudi to delay the attack, but were rebuffed by the Gulf states convinced that the assault will not be as bloody, or as prolonged, as the aid agencies predict.

The civil war in Yemen has killed about 10,000 people over the past three years and created what the UN says is the world's worst humanitarian disaster.